1. Field of the Invention
The present invention relates to a detecting apparatus of a contour of a moving region in a dynamic image which is applied for a control technique, an edition technique and a detection technique of a dynamic image in a multi-media computer system, a compression technique of a dynamic image in a dynamic image communication such as a visual telephone or a distributed meeting system, and a picture editing technique in a broadcasting field or an image manufacturing field.
2. Description of the Related Art
To efficiently display a series of frames of dynamic image changing with time in a displaying unit, picture elements (or pixels) positioned at a contour of a moving region in each of the frames of dynamic image are specified to detect the contour of the moving region for the purpose of distinguishing a moving object positioned in the moving region. Therefore, two types of detecting apparatuses for detecting a contour of a moving region have been conventionally known. A first type of detecting apparatus is based on the calculation of an optical flow of a dynamic image for each of pixels. The optical flow is a field of vector which shows the dislocation of each pixel point from frame to frame, so that the optical flow denotes a changing speed of the dynamic image. A second type of detecting apparatus is based on a Snake model and the calculation of a spatial energy change in a variable density of each pixel such as light and shade. The Snake model is originally utilized to accurately detect a contour of a static object in a static image, and it is required of a user in the Snake model to manually input an initial contour of a moving region.
2.1. Previously Proposed Art
The first type of detecting apparatus is described with reference to FIG. 1.
As shown in FIG. 1, a first conventional detecting apparatus 11 is provided with an optical flow calculating section 12 for calculating an optical flow of a dynamic image for each of pixels to determine a speed field of the dynamic image, a gradation filter applying section 13 for applying a gradation filtering such as a Gause filtering to the speed field to grade the speed field, and an edge detecting section 14 for detecting an edge of the speed field by applying an edge detecting operator such as a Laplacian filter to the speed field graded in the section 13.
In the above configuration, an optical flow of a dynamic image is initially calculated for each of pixels in the section 12. Therefore, a speed field of the dynamic image is determined. Thereafter, the speed field is graded in the section 13, and the speed field graded is filtered by the edge detecting operator in the section 14. Therefore, an edge of the speed field is detected as a contour of a moving region.
Accordingly, the contour of the moving region in the dynamic image can be accurately detected on condition that the speed field is accurately determined in the section 12.
2.2. Another Previously Proposed Art
The second type of detecting apparatus is described with reference to FIG. 2. In this case, a dynamic image consists of a series of frames of dynamic image.
As shown in FIG. 2, a second conventional detecting apparatus 21 is provided with an initial contour inputting section 22 for inputting an initial contour of a moving region in a frame of dynamic image, a spatial changing energy calculating section 23 for calculating a spatial energy of an contour of the moving region for each of pixels to determine the change of the spatial energies in the contour of the moving region, a contour smoothness calculating section 24 for calculating the smoothness of a curvature of the contour of the moving region, a contour renewing section 25 for repeatedly renewing the contour of the moving region to reduce the change of the spatial energies determined in the section 23 while maintaining the smoothness of the contour of the moving region calculated in the section 24, a locally minimized spatial energy change judging section 26 for judging whether or not the change of the spatial energies of the renewed contour is locally minimized, and a contour outputting section 27 for outputting the renewed contour of the moving region when it is judged in the judging section 26 that the change of the spatial energies is locally minimized. The renewed contour is also input to the inputting section 22 as an initial contour of a moving region in a succeeding frame of dynamic image to repeatedly determine an output line of a succeeding moving region in the succeeding frame of dynamic image.
In the above configuration, an initial contour of a moving region in an initial frame of dynamic image is manually input to the inputting section 22 by an user. Thereafter, the initial contour is renewed in the renewing section 25 to generate a renewed contour of the moving region in the initial frame of dynamic image, and the renewed contour is repeatedly renewed in the renewing section 25. In this case, the change of the spatial energies of the renewed contour is determined in the section 23 each time the renewed contour is renewed again, and the renewed contour is repeatedly renewed to reduce the change of the spatial energies of the renewed contour. Also, the smoothness of the renewed contour is calculated in the section 24 each time the renewed contour is renewed again, and the smoothness of the renewed contour is maintained.
When the change of the spatial energies of the renewed contour is locally minimized, the change of the spatial energies locally minimized is judged in the judging section 26. Therefore, the repeated operation performed in the renewing section 25 is stopped, and the renewed contour finally obtained in the renewing section 25 is output to the outputting section 27 as a calculated contour of the moving region in the initial frame of dynamic image. In other words, the contour of the moving region in one of the frames of dynamic image is detected.
Thereafter, the renewed contour of the moving region in the initial frame of dynamic image is input to the inputting section 22 as an initial contour of a succeeding moving region in a succeeding frame of dynamic image to calculate a contour of the succeeding region in the succeeding frame of dynamic image. Therefore, contours of succeeding frames of dynamic image can be detected by repeatedly performing the procedure in the sections 22 to 27.
Accordingly, moving regions in a series of frames of dynamic image can be obtained on condition that a contour of a moving region in an initial frame of dynamic image is manually input to the inputting section 22 by an user.
2.3. Problems to be Solved by the Invention
However, the speed field of the dynamic image cannot be stably determined in the calculating section 12 of the first type of detecting apparatus 11. Therefore, because the operations in the sections 13, 14 are performed on the basis of the speed field unstably determined in the calculating section 12, there is a drawback that the contour of the moving region cannot be reliably detected.
Also, optical flow information inherently determined for a dynamic image is not utilized in the second type of detecting apparatus 21, and it is required of a user to manually input a contour of a moving region in an initial frame of dynamic image. Therefore, there is a drawback that the application of the detecting apparatus 21 is limited.
In addition, the spatial energy changes in the variable densities of the pixels such as light and shade are utilized as image information in the second type of detecting apparatus 21, and there is a rapid change of a variable density not corresponding to a contour of a moving region in a general situation. Therefore, it is required that a supposed contour of a moving region in an initial frame of dynamic image input to the inputting section 22 is set to positions near to a true contour of the moving region. Accordingly, it is difficult to strictly input a supposed contour of a moving region for the purpose of detecting the contour of the moving region according to the Snake model.